Pollution Charaterization And Source Apportionment Of Vocs In Chengdu Urban Air

In this study,concentrations of volatile organic compounds（VOCs）were continuously observed at urban area of Chengdu from February 2016 to March 2017 by TH-PKU₃00B volatile organic compounds online monitoring instruments.Combined with the data of meteorological factors during the same period,the pollution characteristics,chemical reactivity and formation potential of secondary organic aerosols（SOA）of VOCs were investigated.Furthermore,positive matrix factorization（PMF）receptor model was applied to analyze the source contribution of VOCs in four seasons.The results show that the average hours of VOCs in air volume fraction of 53.39×10-9,the largest share of air VOCs are alkanes,accounting for 45.85 percent,followed by aromatics（16.14%）,alkyne（16.14%）,olefins（13.38%）and halocarbons（8.62%）.Major species with larger volume concentration include C2^C5 alkanes,acetylene,ethylene,benzene series and dichloromethane.The monthly average concentration of VOCs display bimodal distribution,the greatest value in December,the lowest in June.In addition,their concentrations showed a seasonal pattern with the highest values in winter,followed by fall,summer and spring.The diurnal variation curve of TVOCs,alkanes,olefins and alkyne have same characteristics with the three peaks appearing in the rush hours with heavy traffic,indicating that VOCs in air in Chengdu city were significantly affected by vehicle emissions and fuel combustion.The meteorologic conditions had significant influence on the VOCs.When east or southeast winds blow in Chengdu,there is lower occurrence of concentrations of VOCs,while west or southwest winds could lead to higher concentrations because of the emission of industrial sources.OH loss rate and ozone formation potentials（OFPs）were estimated to assess the relative effects of each VOC species on ozone formation.The results show that the average ·OH radical loss rate constant value of VOCs was 8.76×10-12cm3·molecule-1·s-1 while the mixing incremental reactivity value was 2.76mol·mol-1.It means that the chemical reactivity of atmospheric VOCs was stronger.The alkenes volumetric fraction was far less than alkanes while the chemical reactivity contribution rate was high.Chengdu urban air VOCs key active ingredient is a C2^C5 olefins,acetylene,toluene,m/p-xylene and other aromatic hydrocarbons.The SOA concentration values obtained by the fractional aerosol coefficients（FAC）were 1.86μg/m3,as the largest contributor,aromatic hydrocarbons accounted for 97.31% and BTEX are the dominant species.The SOA of VOCs showed a seasonal pattern with the highest values in fall,followed by winter,spring and summer.The results from different seasons of receptor model showed that industrial emissions and vehicle emissions were main sources of VOCs in Chengdu.By applying the positive matrix factorization（PMF）model,five major sources were extracted to identify the sources of VOCs in Chengdu,including industrial emissions（28.39%）,vehicle exhaust（27.01%）,fuel evaporation（18.63%）,paint/solvent usage（15.49%）and biomass burning（10.28%）.